前言

DNS协议作为着互联网客户端-服务器通信模式得第一关，在当下每天都有成千上亿上网记录产生得当今社会，其重要性自然不可言喻。在国内比较有名得DNS服务器有电信得114.114.114.114、阿里云得223.5.5.5，DNSPod得119.29.29.29，配置一个好的DNS服务器可以缩短请求响应时间、降低DNS劫持概率，提升上网体验。

上面这些都是互联网公用DNS服务器，本文博主教大家使用 Java Netty 自建DNS代理服务器，目前网上对于使用Netty自建DNS服务器得教程良莠不齐，大多没有代理步骤，达不到博主想要得代理效果，因而创建此文。觉得本文有帮助得可以关注博主

• github.com/wayn111

一、自建DNS代理服务器有哪些优势

1. 域名控制：对于特定域名可以自由控制访问权限（屏蔽对特定网站访问）
2. 域名记录：记录局域网内各个主机得域名访问（记录员工上网记录）
3. 配置内网域名：通过自建DNS服务器可以配置内网域名，节约成本
4. DNS负载均衡：通过自建DNS服务器可以轻松实现对于访问域名得负载均衡配置
5. CDN网络：返回距离客户端最近的可用IP
6. …

二、自建DNS代理服务器代码

1. 添加域名黑名单文件，Maven项目在 resources 文件夹下添加 black_list.txt 文件，注意域名最后的 .，在 Netty 自带的DNS查询Handler中，报文返回的域名最后都是带 . 的。实际上每个域名后都有一个 .，它表示根域名，通常它都是被隐藏的。

// 添加域名黑名单
google.com.
facebook.com.

接着解析 black_list.txt 文件，初始化内容放入 BLACK_LIST_DOMAIN

private static final List<String> BLACK_LIST_DOMAIN = new ArrayList<>();
    static {
        String s;
        try (InputStream is = DnsServer.class.getClassLoader().getResourceAsStream("black_list.txt");
             BufferedReader br = new BufferedReader(new InputStreamReader(is))) {
            while (StrUtil.isNotBlank(s = br.readLine())) {
                BLACK_LIST_DOMAIN.add(s);
            }
        } catch (Exception e) {
            log.error(e.getMessage(), e);
        }
    }

2. 使用UDP协议绑定本机53端口（DNS协议默认使用UDP 53端口），并初始化 ProxyUdp DNS请求代理对象

@Slf4j
public final class DnsServer {
    private static final List<String> BLACK_LIST_DOMAIN = new ArrayList<>();
    static {
       ...
    }

    public static void main(String[] args) throws Exception {
        ProxyUdp proxyUdp = new ProxyUdp();
        proxyUdp.init();
        final int[] num = {0};
        final NioEventLoopGroup group = new NioEventLoopGroup();
        Bootstrap bootstrap = new Bootstrap();
        bootstrap.group(group).channel(NioDatagramChannel.class)
                .handler(new ChannelInitializer<NioDatagramChannel>() {
                    @Override
                    protected void initChannel(NioDatagramChannel nioDatagramChannel) {
                        nioDatagramChannel.pipeline().addLast(...);
                    }
                }).option(ChannelOption.SO_BROADCAST, true);

        int port = 53;
        ChannelFuture future = bootstrap.bind(port).addListener(future1 -> {
            log.info("server listening port:{}", port);
        });

        future.channel().closeFuture().addListener(future1 -> {
            if (future.isSuccess()) {
                log.info(future.channel().toString());
            }
        });
    }
}

3. 给 nioDatagramChannel.pipeline() 添加多个 ChannelHandler 对象，接受DNS查询报文以及发送DNS响应报文。划重点来了 在 new SimpleChannelInboundHandler<DatagramDnsQuery>() 中解析客户端发送DNS查询报文, 获取访问域名信息，如果访问域名在黑名单中，则通过 getDatagramDnsResponse() 方法直接返回 192.168.1.1 的DNS响应报文，反之则通过 proxyUdp 对象转发DNS查询。

nioDatagramChannel.pipeline().addLast(new DatagramDnsQueryDecoder());
                        nioDatagramChannel.pipeline().addLast(new SimpleChannelInboundHandler<DatagramDnsQuery>() {
                            @Override
                            protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsQuery msg) {
                                try {
                                    DefaultDnsQuestion dnsQuestion = msg.recordAt(DnsSection.QUESTION);
                                    String name = dnsQuestion.name();
                                    log.info(name + ++num[0]);
                                    Channel channel = ctx.channel();
                                    int id = msg.id();
                                    channel.attr(AttributeKey.<DatagramDnsQuery>valueOf(String.valueOf(id))).set(msg);
                                    if (BLACK_LIST_DOMAIN.contains(name)) {
                                        DnsQuestion question = msg.recordAt(DnsSection.QUESTION);
                                        DatagramDnsResponse dnsResponse = getDatagramDnsResponse(msg, id, question);
                                        channel.writeAndFlush(dnsResponse);
                                        return;
                                    }
                                    proxyUdp.send(name, msg.id(), channel);
                                } catch (Exception e) {
                                    log.error(e.getMessage(), e);
                                }
                            }

                            private DatagramDnsResponse getDatagramDnsResponse(DatagramDnsQuery msg, int id, DnsQuestion question) {
                                DatagramDnsResponse dnsResponse = new DatagramDnsResponse(msg.recipient(), msg.sender(), id);
                                dnsResponse.addRecord(DnsSection.QUESTION, question);
                                DefaultDnsRawRecord queryAnswer = new DefaultDnsRawRecord(
                                        question.name(),
                                        DnsRecordType.A, 600, Unpooled.wrappedBuffer(new byte[]{(byte) 192, (byte) 168, 1, 1}));
                                dnsResponse.addRecord(DnsSection.ANSWER, queryAnswer);
                                return dnsResponse;
                            }

                            @Override
                            public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) {
                                log.error(e.getMessage(), e);
                            }
                        });
                        nioDatagramChannel.pipeline().addLast(new DatagramDnsResponseEncoder());

4. ProxyUdp 作为DNS查询代理类会通过 send(String domain, int id, Channel serverChannel) 方法传入DnsServer类收到的访问域名、DNS事务ID、serverChannel。随后包装访问域名请求DNS服务器114.114.114.114，最后通过 new SimpleChannelInboundHandler<DatagramDnsResponse>() 将收到的DNS响应报文通过上一步传入得 serverChannel 输出到客户端。

@Slf4j
class ProxyUdp {
    private Channel serverChannel;
    private Channel proxyChannel;

    public void init() throws InterruptedException {
        EventLoopGroup proxyGroup = new NioEventLoopGroup();
        Bootstrap b = new Bootstrap();
        b.group(proxyGroup)
                .channel(NioDatagramChannel.class)
                .handler(new ChannelInitializer<DatagramChannel>() {
                    @Override
                    protected void initChannel(DatagramChannel ch) {
                        ChannelPipeline p = ch.pipeline();
                        p.addLast(new DatagramDnsQueryEncoder())
                                .addLast(new DatagramDnsResponseDecoder())
                                .addLast(new SimpleChannelInboundHandler<DatagramDnsResponse>() {
                                    @Override
                                    public void channelActive(ChannelHandlerContext ctx) {
                                        log.info(ctx.channel().toString());
                                    }

                                    @Override
                                    protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsResponse msg) {
                                        DatagramDnsQuery dnsQuery = localChannel.attr(AttributeKey.<DatagramDnsQuery>valueOf(String.valueOf(msg.id()))).get();
                                        DnsQuestion question = msg.recordAt(DnsSection.QUESTION);
                                        DatagramDnsResponse dnsResponse = new DatagramDnsResponse(dnsQuery.recipient(), dnsQuery.sender(), msg.id());
                                        dnsResponse.addRecord(DnsSection.QUESTION, question);

                                        for (int i = 0, count = msg.count(DnsSection.ANSWER); i < count; i++) {
                                            DnsRecord record = msg.recordAt(DnsSection.ANSWER, i);
                                            if (record.type() == DnsRecordType.A) {
                                                // just print the IP after query
                                                DnsRawRecord raw = (DnsRawRecord) record;
                                                DefaultDnsRawRecord queryAnswer = new DefaultDnsRawRecord(
                                                        question.name(),
                                                        DnsRecordType.A, 600, Unpooled.wrappedBuffer(ByteBufUtil.getBytes(raw.content())));
                                                dnsResponse.addRecord(DnsSection.ANSWER, queryAnswer);
                                            }
                                        }

                                        serverChannel.writeAndFlush(dnsResponse);
                                    }

                                    @Override
                                    public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) {
                                        log.error(e.getMessage(), e);
                                    }
                                });

                    }
                });
        proxyChannel = b.bind(0).sync().addListener(future1 -> {
            log.info("绑定成功");
        }).channel();
    }

    public void send(String domain, int id, Channel serverChannel) {
        this.serverChannel = serverChannel;
        DnsQuery query = new DatagramDnsQuery(null, new InetSocketAddress("114.114.114.114", 53), id).setRecord(
                DnsSection.QUESTION,
                new DefaultDnsQuestion(domain, DnsRecordType.A));
        this.proxyChannel.writeAndFlush(query);
    }
}

5. 客户端请求DNS代理服务器流程图如下

6. 自建DNS服务器全部代码

@Slf4j
public final class DnsServer {
    private static final List<String> BLACK_LIST_DOMAIN = new ArrayList<>();
    static {
        String s;
        try (InputStream is = DnsServer.class.getClassLoader().getResourceAsStream("black_list.txt");
             BufferedReader br = new BufferedReader(new InputStreamReader(is))) {
            while (StrUtil.isNotBlank(s = br.readLine())) {
                BLACK_LIST_DOMAIN.add(s);
            }
        } catch (Exception e) {
            log.error(e.getMessage(), e);
        }
    }

    public static void main(String[] args) throws Exception {
        ProxyUdp proxyUdp = new ProxyUdp();
        proxyUdp.init();
        final int[] num = {0};
        final NioEventLoopGroup group = new NioEventLoopGroup();
        Bootstrap bootstrap = new Bootstrap();
        bootstrap.group(group).channel(NioDatagramChannel.class)
                .handler(new ChannelInitializer<NioDatagramChannel>() {
                    @Override
                    protected void initChannel(NioDatagramChannel nioDatagramChannel) {
                        nioDatagramChannel.pipeline().addLast(new DatagramDnsQueryDecoder());
                        nioDatagramChannel.pipeline().addLast(new SimpleChannelInboundHandler<DatagramDnsQuery>() {

                            @Override
                            protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsQuery msg) {
                                try {
                                    DefaultDnsQuestion dnsQuestion = msg.recordAt(DnsSection.QUESTION);
                                    String name = dnsQuestion.name();
                                    log.info(name + ++num[0]);
                                    Channel channel = ctx.channel();
                                    int id = msg.id();
                                    channel.attr(AttributeKey.<DatagramDnsQuery>valueOf(String.valueOf(id))).set(msg);
                                    if (BLACK_LIST_DOMAIN.contains(name)) {
                                        DnsQuestion question = msg.recordAt(DnsSection.QUESTION);
                                        DatagramDnsResponse dnsResponse = getDatagramDnsResponse(msg, id, question);
                                        channel.writeAndFlush(dnsResponse);
                                        return;
                                    }
                                    proxyUdp.send(name, msg.id(), channel);
                                } catch (Exception e) {
                                    log.error(e.getMessage(), e);
                                }
                            }

                            private DatagramDnsResponse getDatagramDnsResponse(DatagramDnsQuery msg, int id, DnsQuestion question) {
                                DatagramDnsResponse dnsResponse = new DatagramDnsResponse(msg.recipient(), msg.sender(), id);
                                dnsResponse.addRecord(DnsSection.QUESTION, question);

                                // just print the IP after query
                                DefaultDnsRawRecord queryAnswer = new DefaultDnsRawRecord(
                                        question.name(),
                                        DnsRecordType.A, 600, Unpooled.wrappedBuffer(new byte[]{(byte) 192, (byte) 168, 1, 1}));
                                dnsResponse.addRecord(DnsSection.ANSWER, queryAnswer);
                                return dnsResponse;
                            }

                            @Override
                            public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) {
                                log.error(e.getMessage(), e);
                            }
                        });
                        nioDatagramChannel.pipeline().addLast(new DatagramDnsResponseEncoder());

                    }
                }).option(ChannelOption.SO_BROADCAST, true);

        int port = 53;
        ChannelFuture future = bootstrap.bind(port).addListener(future1 -> {
            log.info("server listening port:{}", port);
        });

        future.channel().closeFuture().addListener(future1 -> {
            if (future.isSuccess()) {
                log.info(future.channel().toString());
            }
        });
    }
}

@Slf4j
class ProxyUdp {
    private Channel localChannel;
    private Channel proxyChannel;

    public void init() throws InterruptedException {
        EventLoopGroup proxyGroup = new NioEventLoopGroup();
        Bootstrap b = new Bootstrap();
        b.group(proxyGroup)
                .channel(NioDatagramChannel.class)
                .handler(new ChannelInitializer<DatagramChannel>() {
                    @Override
                    protected void initChannel(DatagramChannel ch) {
                        ChannelPipeline p = ch.pipeline();
                        p.addLast(new DatagramDnsQueryEncoder())
                                .addLast(new DatagramDnsResponseDecoder())
                                .addLast(new SimpleChannelInboundHandler<DatagramDnsResponse>() {
                                    @Override
                                    public void channelActive(ChannelHandlerContext ctx) {
                                        log.info(ctx.channel().toString());
                                    }

                                    @Override
                                    protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsResponse msg) {
                                        DatagramDnsQuery dnsQuery = localChannel.attr(AttributeKey.<DatagramDnsQuery>valueOf(String.valueOf(msg.id()))).get();
                                        DnsQuestion question = msg.recordAt(DnsSection.QUESTION);
                                        DatagramDnsResponse dnsResponse = new DatagramDnsResponse(dnsQuery.recipient(), dnsQuery.sender(), msg.id());
                                        dnsResponse.addRecord(DnsSection.QUESTION, question);

                                        for (int i = 0, count = msg.count(DnsSection.ANSWER); i < count; i++) {
                                            DnsRecord record = msg.recordAt(DnsSection.ANSWER, i);
                                            if (record.type() == DnsRecordType.A) {
                                                // just print the IP after query
                                                DnsRawRecord raw = (DnsRawRecord) record;
                                                DefaultDnsRawRecord queryAnswer = new DefaultDnsRawRecord(
                                                        question.name(),
                                                        DnsRecordType.A, 600, Unpooled.wrappedBuffer(ByteBufUtil.getBytes(raw.content())));
                                                dnsResponse.addRecord(DnsSection.ANSWER, queryAnswer);
                                            }
                                        }

                                        localChannel.writeAndFlush(dnsResponse);
                                    }

                                    @Override
                                    public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) {
                                        log.error(e.getMessage(), e);
                                    }
                                });

                    }
                });
        proxyChannel = b.bind(0).sync().addListener(future1 -> {
            log.info("绑定成功");
        }).channel();
    }

    public void send(String domain, int id, Channel localChannel) {
        this.localChannel = localChannel;
        DnsQuery query = new DatagramDnsQuery(null, new InetSocketAddress("114.114.114.114", 53), id).setRecord(
                DnsSection.QUESTION,
                new DefaultDnsQuestion(domain, DnsRecordType.A));
        this.proxyChannel.writeAndFlush(query);
    }
}

三、本地测试

1. 修改本机DNS设置(win11)，修改首选、备选DNS地址为127.0.0.1
2. 打开命令行工具，执行DNS缓存清除命令 ipconfig/flushdns
3. 打开浏览器访问常用网站，控制台输出如下

自此，自建的DNS代理服务器就可以正常使用了

参考资料

• 用 Node.js 手写一个 DNS 服务器
• DNS中有哪些值得学习的优秀设计
• netty dns example